Well, you really have to play well in premium vehicles in order to get good RP gain, but with a T4 premium tank, if you're good, you can unlock a T2 vehicle in one game, especially if it's the first win of the day (and/or if you have premium account).
Right now, as I said earlier, I'm back at playing WoT, and I think I have found my two new favourites: The Sherman III at tier 5 and the Charioteer at tier 8. Especially the Charioteer. Man, what a gun. You can just tear through enemy teams if you are half decent laughing, even though viewrange is a bit lacking. But apart from that, it's a beast. An absolute mondter of a TD.

I'm dabbling in TDs on both games but haven't decided if I like them or not. How limited is the traverse on the Charioteer? That's my main issue with them so far, however in WoT mobile the whole machine rotates with your "camera" view, just like the turret of a tank normally does, so its kind of moot there. I test drove an SU76 in WT and was impressed. My problem is that I tend to take A LOT of hits, so I need something that can withstand my beating. I do prefer to play as a sniper though, so from that side TDs fit my style.
I'm loving the M13 and M16 gun carriages in WT right now. I love the speed and maneuverability on them, their firepower is impressive given their armament, and with artillery researched they are capable of scoring tons of hits. My favorite tactic is to sweep wide with one, get a good spot of the enemies flank, blast them with artillery, then duck down before they can spot me. I like to think of myself as a disruptor in that role, causing mayhem to to enemy so my teams heavy armor can move in and paste them while they are,distracted with me.
I would really love it if WT would incorporate infantry into the game more. I think it would add to the realism and give players more options and different objectives. I'm no game programmer, but I wouldn't think it would be too hard to add that feature.